1. Field of the Invention
The present invention relates to a heat treat furnace, such as a drying furnace or a curing oven, and more particularly, it relates to the structure of a furnace for heat treating plate type workpieces.
2. Description of the Related Art
In order to simultaneously apply electrodes to end portions of a number of chip components, a holding plate is generally employed for elastically holding the chip components, as disclosed in U.S. Pat. No. 4,395,184. This holding plate comprises a hard substrate which is provided on its center with a thin flat plate portion having a number of through holes and a rubber-like elastic member embedded in a cavity defined by the flat plate portion and provided with receiving holes passing through the portions corresponding to the through holes.
When external electrodes are formed at the end portions of chip components by using such a holding plate, the chip components are held by the receiving holes so that they are partially upwardly projected from the plate. Then the plate is placed on a conveyor and carried to pass under a roll which is coated with electrode paste. Thus, the electrode paste is applied to the projected portions of the chip components, and then the plate is conveyed under heating means, so that the electrode paste is heated and dried.
In the case of such heating means, the electrode paste can be applied to the chip components and then dried while the components remain on the same conveyor. However, since the heating means is installed along the direction for carrying the plate, the installation space must be increased, resulting in inferior efficiency in the drying step.
Alternatively, it is possible to provide a batch type drying furnace in an intermediate portion of such a conveyor so that a plurality of holding plates carried by the conveyor are simultaneously inserted into the drying furnace to be subjected the prescribed drying and then discharged from this furnace. In this case, however, it is necessary to keep the plates in a waiting state for a certain time since only a certain number of plates continuously carried on the conveyor can be collectively inserted in the drying furnace at one time. This leads to waste of time.
It is also possible to replace the aforementioned batch type drying furnace with a vertical conveyor so that externally carried holding plates are inserted one by one onto the vertical conveyor to be subjected to continuous drying. In this case, the treatment time can be reduced since there is no need to keep the plates in a waiting state, and the installation floor space can be reduced by virtue of the vertical conveyor. However, the conveyor structure in the furnace is complicated and the chip components are vibrated during passage through the furnace dropped from the receiving holes of the plates.